The process by which material is expelled from a galaxy's nucleus and accelerated, often involving cosmic rays and dust.Galactic outflow acceleration is the process by which gas, dust, and cosmic rays are expelled from a galaxy's central regions and accelerated to high velocities, often forming large-scale winds that can extend far beyond the galactic disk. These outflows are typically driven by intense star formation, supernova explosions, or the activity of a supermassive black hole at the galaxy's core. The accelerated material can carry energy and heavy elements into the intergalactic medium, influencing the galaxy's evolution by removing gas that would otherwise form new stars and enriching the surrounding environment.
The concept of galactic outflows has been developed over several decades, with early observations in the 1960s and 1970s revealing gas moving at high velocities in the halos of galaxies. The role of cosmic rays in driving these outflows was proposed in the 1980s and has been refined through subsequent theoretical work and simulations.
The acceleration mechanism involves a combination of thermal pressure from supernova explosions, radiation pressure from hot young stars, and cosmic rays that couple to the gas via magnetic fields. Cosmic rays, being charged particles, can stream through the galaxy and transfer momentum to the surrounding gas through collisions and magnetic field interactions, effectively pushing the material outward. In the case of active galactic nuclei, relativistic jets and intense radiation from the accretion disk around the black hole can also drive outflows, accelerating material to speeds of hundreds to thousands of kilometers per second.
Understanding galactic outflow acceleration is crucial for modeling galaxy formation and evolution, as well as for interpreting observations of the circumgalactic medium in large-scale surveys.
Some galactic outflows are so powerful that they can eject material from the galaxy entirely, escaping into intergalactic space and carrying heavy elements over millions of light-years.
| Ṁ_out | variable | Mass outflow rate — mass flow rate kilogram per second |
| ρ | variable | Mass density of the outflowing material — mass density kilogram per cubic metre |
| v | variable | Flow velocity perpendicular to the area — velocity metre per second |
| A | variable | Cross-sectional area through which material flows — area square metre |
| v_{\rm term} | variable | Terminal outflow velocity — velocity metre per second |
| \dot{m} | variable | Mass accretion rate — mass accretion rate kilogram per second |















